Robotic position calibration is a problem in automation systems using robots. The most common calibration of the desired positions for robots is done manually. For 3-axis or polar robots, calibration can be achieved using the motion pendants provided by the robot manufacturer. In wafer processing, 3-axis robots can locate the height of a wafer and find the correct x-and y coordinates of the center. For 6-axis robots, the additional degrees of freedom create desired flexibility to adjust the end effectors for three angular positions. However, greater flexibility requires greater complexity of calibration since angular positions must be calibrated for each of the stations in addition to the height and center location. Robots typically use end effectors, which are devices or tools connected to the end of a robot arm. In wafer processing systems, such as CMP, stations are locations systems where wafer's are picked up or placed.
Robots are calibrated to safely move delicate silicon wafers to and from several positions or stations within the CMP tool and to and from cassettes or pods where groups of wafers are input or taken from the tool. While locations of the robot and stations are roughly known within a general area, the exact location and orientation varies between each end effectors due to the accumulation of manufacturing tolerances. Distortions during end effectors shipping or robot “crashes” into CMP tool frames also dislocate the original orientation. Thus, precision robot station calibration is required for reliable and safe handling of expensive semiconductor wafers.
Manual calibration by an expert can take days and has many drawbacks. Manual calibration is dependent upon the vision and visual access of the skilled expert. Furthermore, manual calibration is time-consuming, costly and inconsistent. Sometimes tool geometry makes safe observation of robot motions difficult or impossible.